Acute arthritis or trauma may necessitate the replacement of natural bones and joints with prosthetic devices. For example, the replacement of the hip joint is one of the more common operations performed for these reasons. Such procedures have become somewhat commonplace in the treatment of acute arthritis or trauma not only in human beings but also in animals such as dogs and cats.
With respect to implantation of a hip prosthesis, rigid fixation of femoral components is desirable to promote long term stabilization and also to minimize the occurrence of adverse symptoms after surgery, such as pain and limp. Such fixation is also desirable to minimize bone-implant micromotion.
One known method of prosthesis fixation involves the use of cement. However, in time cement can loosen with undesired results. Such results and other undesirable effects from cement use are described in U.S. Pat. No. 4,406,023.
In an attempt to achieve such rigid fixation but without cement, hip prostheses have been inserted into bone canals to obtain a press-fit arrangement. A review of known hip implants is presented in Noble et al., "The Myth of `Press-Fit` in the Proximal Femur," America Academy of Orthopedic Surgeons 55th Annual Meeting, Atlanta, Ga., Feb. 4-9, 1988, which is incorporated herein in its entirety by reference.
However, some of the shortcomings of these hip implants include that they are stabilized by contact with cortical bone in separate regions of the medullary canal and that the interfaces do not constitute a press-fit.
Secondly, rigid fixation is also dependent on the surface texture of the hip implant which is press-fit into the medullary canal. A typical finish in known devices includes a satin or sand-blasted finish. But this surface is not acceptable if implant micromotion is to be minimized. A fuller discussion of surface texture is set forth in E. Kamaric, P.C. Noble and J.W. Alexander, "The Effect of Proximal Surface Texture on the Acute Stability of Cementless Fixation", a copy of which is submitted herewith and incorporated in its entirety.
We have invented an improved bone prosthesis which overcomes the aforementioned problems and provides for more rigid fixation within the intramedullary canal of a bone.